The present invention relates to telephony systems that use a common channel signaling protocol and more particularly, to a system and method for predictive dialing in a telephony system using Integrated Digital Services Network (ISDN) protocol.
Integrated Services Digital Network (ISDN) is a set of digital transmission protocols defined by CCITT (the Consultative Committee for International Telephone and Telegraphy). ISDN allows data (typically digitized voice signals) to be transmitted simultaneously across the world using end to end digital connectivity, with signaling carried separately from voice/data. In the analog network used by the Plain Old Telephone System (POTS), a two wire loop from the telephone company""s local central office to the customer premises supports a single transmission channel for carrying only one service, such as voice, data or video, at a time. With ISDN, the same pair of twisted copper wires is logically divided into multiple channels.
ISDN defines two types of logical channels, distinguished by function and capacity. Bearer channels (or B channels) carry voice or data occupying a band width of 64 Kbps (or a multiple of 64 Kbps). A data channel (or D channel) handles signaling. Currently, there are two common types of ISDN services: basic rate interface (BRI) and primary rate interface (PRI). BRI consists of two 64 Kbps B channels and one 16 Kbps D channel for a total of 144 Kbps. PRI is intended for users with greater capacity requirements and includes 23 B channels plus one 64 Kbps D channel for a total of 1,536 Kbps, typically provided over a T1 line. Other combinations can also be used such as PRI-E1 or T3.
Fractional T1 spans are also available, for example, providing 15 channels including 14 B channels and 1 D channel. Also, multiple T1""s can be configured to share a single D channel. Three T1 spans, for example, could provide 71 B channels plus 1 D channel, centralizing all signaling. Digital transmission of voice or data can also be implemented with an in-channel signaling method called robbed bit signaling. Using this method, voice is digitized and the least significant bit is used to pass signaling information.
Because of the increased data capacity of ISDN and the ability of ISDN to handle all types of information including voice and data, many types of telephony systems have begun to use ISDN. In particular, ISDN is useful in a telephone call center where voice and data communications must be established with a number of agents or operators in the call center. A typical call center is used for telemarketing or collections and automates the outbound dialing and connection of called parties (e.g. customers or potential customers) to the agents in the call center.
Most call centers use predictive dialing or call pacing techniques in which the number of outbound calls being placed exceeds the number of available agents, to maximize the use of the agents by ensuring that all available agents have a call to answer. In a conventional call center, a ratio of telephone (or trunk) lines to agents is established; for example, a ratio of 2:1 provides two trunk lines for every one agent. The ratio can be adjusted using call pacing algorithms to maximize the use of. agents while also ensuring that answered calls are not placed on hold for an extensive period of time. One example of a call pacing algorithm is disclosed in greater detail in U.S. Pat. No. 5,295,184 entitled DYNAMICALLY ADJUSTABLE CALL PACING SYSTEM, assigned to the assignee of the present invention and incorporated herein by reference.
When the conventional predictive dialing techniques are used with ISDN, the use of the bearer channels is not maximized because of the way in which calls are made using ISDN. A telephone call is typically made using ISDN by allocating a B channel in advance, sending the telephone number on the D channel, and waiting to see if the other party is available. If a connection is not made, the line is dropped and the allocated B channel can eventually be allocated to another call. Allocating a bearer channel in advance for each telephone number dialed results in wasted ISDN resources. If a number is dialed, for example, and no connection is made to the called party, the bearer channel allocated to that number is not utilized unti re-allocated to a number where a connection is made. Many existing ISDN specs actually prohibit the allocation of bearer channels in advance.
Accordingly, a need exists for a method of maximizing the use of bearer channels when using ISDN, ATM or another common channel signaling protocols for predictive dialing in a telephony system. A need also exists for a telephony system in which the cost of the number of ISDN lines required to support the telephony system or call center is reduced.
The present invention features a method for dialing in a telephony system using a common channel signaling protocol having at least one data channel for carrying data signals and a plurality of bearer channels for carrying voice signals. The method comprises determining predictive dialing factors and determining the number of telephone numbers to be dialed according to the predictive dialing factors and a predictive dialing algorithm. The number of telephone numbers to be dialed exceeds the number of bearer channels. Dialing commands are then transmitted over the data channel for the number of telephone numbers to be dialed independently of the number of bearer channels.
According to one embodiment, the common channel signaling protocol is an integrated services digital network (ISDN) protocol. The ISDN protocol includes a primary rate interface connection having one (1) data channel a twenty-three (23) bearer channels. In another embodiment, the common channel signaling protocol is an asynchronous transfer mode (ATM) protocol.
According to one method, the steps of determining the number of telephone numbers to be dialed and transmitting the dialing commands are performed continuously in a call pacing mode. The step of determining the predictive dialing factors can also be performed continuously to dynamically update the predictive dialing factors. According to another method, the steps of determining the number of telephone numbers to be dialed and transmitting the dialing commands are performed at least once in a burst dialing mode. The method can also include the step of tracking call statistics such that the predictive dialing factors are determined from the statistics. The predictive dialing factors include an anticipated connect ratio, an average talk time, an agent pool size, a number of idle agents, a number of calls on hold, and an average hold time.
The present invention also features a telephony system for predictive dialing using the common channel signaling protocol. The telephony system comprises a telephony control/manager for determining the predictive dialing factors and for determining a number of telephone numbers to be dialed according to the predictive dialing factors. The telephony system also comprises a dialing switch, connected to the control/manager and to the data channel and the bearer channels, for transmitting dialing commands for the number of telephone calls to be dialed over the data channel to a central office switch and for switching answered calls to available bearer channels.